Choosing ADVPN support method

The difference between the two presented ADVPN support methods is summarized in the following diagram:

• Both methods rely on the exchange-ip-addrv4 feature to inject the /32 loopback route through the shortcut.

• In the RR-based design, the Hubs reflect the LAN prefixes between Spokes, and the Spokes then use the injected /32 loopback route to recursively resolve the BGP NH of those reflected routes.

• In the RR-less design (with Dynamic BGP), the Spokes use the injected /32 loopback route to establish a BGP session between them over the shortcut, which is then used to exchange the LAN prefixes directly.

As a rule of thumb, Dynamic BGP is recommended for most of the new deployments for the following reasons:

• Eliminating the need for BGP Route Reflection greatly improves the scalability of the solution, which removes the scaling bottleneck from the Hubs.

• It also greatly simplifies the routing design, allowing route summarization on the Hubs, both within the region and— even more crucially—between the regions.

Nevertheless, there are several use cases in which the traditional RR-based design will be necessary or indeed preferred:

• Existing deployments

• Preserving route attributes